两方程湍流模型对内背风波数值模拟的影响

Effects of a two-equation turbulence model on the simulation of the internal lee waves

为了深入理解非静力近似下的波-湍相互作用问题,本研究在σ坐标的海洋环境研究和预报模型(MERF)中引入常用的Mellor-Yamada两方程湍混合参数化方案(MY2.5),评估垂向湍混合对小尺度背风波传播过程的影响.瞬时状态场的模拟结果表明,无论是否为非静力近似条件,上述湍参数化方案的引入都会减弱背风波传播的模拟效果.从时间平均场的试验结果来看,垂向湍混合过程会显著减小非静力近似和静力近似之间的差异.此外,能量收支分析的诊断结果表明,MY2.5方案会显著抑制陆坡地形下的背风波传播过程,进而将更多的潮能转化到不可逆的湍混合过程中.

In order to understand the wave-turbulence interaction under non-hydrostatic conditions to prepare future ad-vanced very-high-resolution ocean reanalysis data,an𝜎-coordinate ocean model-namely,the Marine Environ-ment Research and Forecasting(MERF)model-with an idealized supercritical slope topography is applied to conduct a series of high-resolution numerical experiments with and without the non-hydrostatic approximation.The popular Mellor-Yamada two-equation turbulence model(MY2.5)is enclosed in MERF to validate its effect on small-scale internal lee waves.Instantaneous results show that the internal lee-wave processes are relaxed through employment of the MY2.5 scheme,whether or not in the non-hydrostatic model.Time averaged results suggest the influences of the vertical mixing parameterization scheme on the numerical results are more dominant than the non-hydrostatic/hydrostatic selection for the large-scale dynamic process.Besides,diagnostic analyses of the energy budget show that the spread of internal lee waves at the slope is dramatically suppressed by the vertical turbulent mixing,indicating more tidal energy is able to be converted into the irreversible mixing when the two-equation turbulence model is employed.